An aircraft's airframe and engines produce varying amounts of objectionable audible noise during different flight conditions. On departure, the engines produce the greatest amount of noise. However, during approach, noise from the airframe is also a significant contributor. Airframe noise is generated by the interaction between the airflow and the aircraft structure. The primary sources include landing gear, and wing leading and trailing edges including the high-lift devices and flap systems. On an approach to landing, the wing leading edge devices and the wing trailing edge flap systems are extended and the engines are operating at relatively low thrust levels. During approach, the dominant noise source is generated by the flap systems when the flaps are extended and the lateral flap edges are exposed.
One of the main noise-generating mechanisms at play in flap edge airflows can be attributed to hydrodynamic fluctuations, e.g., shear layer fluctuations, and their interaction with surrounding edges and surfaces. When an airfoil (e.g., flap) creates lift, the inherent pressure difference between the top and bottom surfaces causes air to escape around the edges of the airfoil in an attempt to equalize the pressure. When a wing flap is deployed during takeoff or landing, the flap is deflected downward and the side edges are exposed. At these edges, a shear flow launches at the side edge from a high treasure region at the bottom surface of the flap, initiating a strong vortex. A similar mechanism occurs at the upper side edge, creating another vortex of lesser strength. As the lower and upper vortices migrate rearward, they expand and eventually converge and strengthen. As they progress, the vortices scrub against adjacent structure, creating sound. Additionally, many flap systems include flaps that have exposed cavities formed in their side edges where the sound can resonate, creating tones that increase objectionable audible noise.
Accordingly, it is desirable to provide wing flaps for aircraft that reduce aerodynamically generated noise from the flap side edges when the flaps are extended, for example, during an approach to landing, aircraft including such flaps, and methods for making such flaps. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.